Quadrupole-driven non-Fermi-liquid and magnetic-field-induced heavy fermion states in a non-Kramers doublet system

Abstract

Orbital degrees of freedom in condensed matter could play important roles in forming a variety of exotic electronic states by interacting with conduction electrons. In $4f$-electron systems, because of strong intra-atomic spin-orbit coupling, an orbitally degenerate state inherently carries quadrupolar degrees of freedom. The present work has focused on a purely quadrupole-active system ${\mathrm{PrIr}}_{2}{\mathrm{Zn}}_{20}$ showing superconductivity in the presence of an antiferroquadrupole order at ${T}_{\mathrm{Q}}=0.11$ K. We observed non-Fermi-liquid (NFL) behaviors emerging in the electrical resistivity $\ensuremath{\rho}$ and the $4f$ contribution to the specific heat, ${C}_{4f}$, in the paramagnetic state at $T > {T}_{\mathrm{Q}}$. Moreover, in magnetic fields $B\ensuremath{\le}6$ T, all data sets of $\ensuremath{\rho}(T)$ and ${C}_{4f}(T)$ are well scaled with characteristic temperatures ${T}_{0}$'s. This observation of the NFL state in the nonmagnetic quadrupole-active system has an origin intrinsically different from that observed in the vicinity of the conventional quantum critical point. It implies possible formation of a quadrupole Kondo lattice resulting from hybridization between the quadrupoles and the conduction electrons with an energy scale of ${k}_{\mathrm{B}}{T}_{0}$. At $T\ensuremath{\le}0.13$ K, $\ensuremath{\rho}(T)$ and ${C}_{4f}(T)$ exhibit anomalies as $B$ approaches 5 T. This is the manifestation of a field-induced crossover toward a Fermi-liquid ground state in the quadrupole Kondo lattice.